LT6010B - An optically controlled high-speed broadband phase modulator - Google Patents

Abstract

The invention is assigned to microwave devices and it is applied to modulate a phase of a propagating electromagnetic (EM) mode. An optically controlled high-speed broadband phase modulator is made up of five main components. Two cylindrical metal waveguides (2), the first of ones is intended to excite the main waveguide mode. The second metal waveguide receives a modulate signal and transmit forward. A semiconductor waveguide (1) ends are placed into the metal waveguides (2) and the working part of the waveguide (1) with a length L is placed to a solenoid (3), which is fixed on the frame (4). The waveguide (1) is made of semiconductor p-type germanium (Ge) whose EM properties depend on a proportion between the heavy hole concentration and the light hole one. The proportion is controlled with a system of light sources (5). The higher modes of the waveguide are the parasitic ones. These modes have the very large attenuation.by changing the light intensity. The main hybrid mode (with the lowest cutoff frequency) only propagates on the semiconductor p-Ge waveguide with a very small attenuation at the certain frequencies normalized to a waveguide radius. The changing of a phase of the main wave of p-Ge waveguide occurs by varying a concentration proportion of heavy and light holes.

Description

The invention relates to microwave devices and is used to modulate the wave phase of a waveguide.

An analogous device was developed by [Babbitt R. W., Stern R. A. Dielectric waveguide ferrite modulator / switch, Authorized Representative (Original Assignee): United States of America as Representative to the Army, Patent US4490700 A, Dec. 25, 1984],

The analogue is a ferrite modulator controlled by a permanent magnetic field. The main parts of the modulator are a square-shaped ferrite rod and a solenoid generating a permanent longitudinal magnetic field. The ferrite rod is housed inside a solenoid and is classified in the dielectric waveguide class. Such a gyrotropic waveguide propagates the main and higher types of hybrid HE _mn and EH _mn waves.

The analog has three fundamental disadvantages. First, it is relatively low bandwidth, since a rectangular cross-section waveguide can propagate a larger number of parasitic waves than a cylindrical waveguide of the same cross-sectional area. The second disadvantage is the low speed of the device, since the change of the controlling magnetic field Ho (Bo = poPrHo) is obtained by changing the current of the solenoid, which makes the control process inert, not fast enough. The third disadvantage is the limited operating frequency range due to the sudden decrease of the ferrite phase change (proportional to the wavelength) in the magnetized ferrite waveguide in the high frequency range. The upper limit of the frequency at _{which the} ferrite phase change can change with H _o is 2/3 of the YAD (ultra high frequency, 30-300 GHz) range. Semiconductor materials do not have these disadvantages.

To avoid the first mentioned disadvantage, a cylindrical waveguide with a standardized radius fr = 0.03-0.1GHz is proposed. At fr <0.03 GHzm, the modulator would be unstable because of the fundamental wave type critical frequency in this area and the phase constant changing too fast with frequency variation. At fr> 0.1 GHz, a large number of higher-order parasitic waves are excited, which are of the same symmetry as the main wave and have a single order loss with the main wave. Therefore, the total modulator losses increase, and furthermore, parasitic wave losses would further and unpredictably modulate and distort the useful signal. Note that in the rectangular plasma semiconductor waveguide of corresponding dimensions, at higher frequencies, a much larger number of higher-grade parasitic waves occur, so that the rectangular waveguide shape degrades the modulator characteristics.

To avoid the second disadvantage mentioned above, it is proposed to replace the ferritic material from which the waveguide is made by a semiconductor germ permeable material (p-Ge). The EM properties of this semiconductor depend on the concentration ratio between the heavy and light holes. Thus, instead of controlling (wavelength Ho) the wavelength of the waveguide, it is suggested to fix the latter magnitude and control by changing the concentrations of the light and heavy holes. This is achieved by switching the holes from one energy band to another by exposing the material to infrared light with a wavelength of ~ 2-10pm in the case of p-Ge (at N ~ 10 ¹⁹ -10 ²² m ' ³ free charge). This optical transition of the holes from one level of the valence band to the next is very fast, in the order of tenths of a picosecond (~ 10 ^'13 s). Data on the speed of this process are taken from the literature [Beregulin EV et al. Mechanisms of energy relaxation under conditions of nonlinear absorption of light in p-type Ge, Sov. phys. Semicond., 16 (2), 1982, p. 179-181]. [Leung CY Enhanced direct-free-hole absorption in picosecond laser-excited Germanium, Kinese Journal of Physics, Vol. 18, N4, 1980, p. 158-171].

To avoid the third disadvantage mentioned above, it is proposed to replace magnetized ferrite with solid state semiconductor plasma. The plasma semiconductor waveguide can operate over the entire YAD range as well as at higher frequencies, such as HAD (Hyper-High Frequency, 300-3000 GHz). For each frequency range the waveguide radius is calculated. In order to obtain the desired EM characteristics of the waveguide, ie to determine the required properties of the material in a given frequency band, the N concentration and / or the size H _{o of the} semiconductor free carriers must be changed accordingly.

The novelty of our optically controlled high speed wideband phase modulator, consisting of an open semiconductor plasma waveguide and a lighting system, is that the cylindrical waveguide is made of hole-permeable germanium (p-Ge), whose EM properties strongly depend on the concentration ratio between heavy and light holes, and this proportion is controlled by changing the light intensity with the help of a light source system.

Brief Description of the Drawings

Fig. Optically Controlled Fast Broadband Phase Modulator Design.

Fig. The dependence of the normalized phase coefficient h'r of the fundamental and higher wave types on the normalized frequency fr in a plasma p-Ge waveguide with εκ = 16, β ₀ = 1 T, N = 5Ί0 ¹⁹ m ′ ³ , m * _h = 0.279m _e , m * i = 0.043m _e , μ \ = 6.3 m ² / V s, μ * ι = 40.9 m ² / Vs for a 70% concentration of heavy holes in the semiconductor.

Fig. The dependence of the normalized attenuation coefficient hr of the basic and higher wave types on the normalized frequency fr in a plasma p-Ge waveguide with εκ = 16, S _o = 1 T, N = 5Ί0 ¹⁹ m ' ³ , m * _h = 0.279m _e , m * i = 0,043m _e , μ \ = 6,3 m ² / V s, μ * ι = 40,9 m ² / V s, with a heavy hole concentration in the semiconductor of 70%.

Fig. The dependence of the phase characteristic h'r (fr) of the main wave type on the relative concentration of heavy holes. The dotted curves correspond to 50%, 55%, 90%, and 95% concentrations of heavy holes, and the dashed lines correspond to 60-90% heavy holes.

The modulator consists of elements: p-Ge waveguide (1); cylindrical waveguides of metal (2); solenoid (3); a dielectric frame (4); a light source system (5); holders (6).

The modulator works this way. Plasma semiconductor cylindrical waveguide is made of conductivity germanium (p-Ge), whose dielectric permeability tensor elements ε _χχ , ε _χγ , ε _savybės , ie properties of EM semiconductor in different directions, strongly depend on the concentration ratio between heavy and light holes. is controlled by a light source system. By changing the intensity of light illuminating the waveguide's working surface, the phase of the waveguide EM wave is changed. Importantly, the normalized radius of the cylindrical plasma p-Ge waveguide is in the range fr = 0.03-0.1 GHz, the heavy hole concentration is varied from 60% to 90% of the total hole concentration in the N waveguide. The modulator is designed for operation at low temperatures and can therefore be used in satellite equipment operating above the Earth's stratosphere (in space).

The relevance and need of the proposed device is confirmed by patents of recent years:

1. [Eu-Jin Andy Lim et al. Optical Modulator and Method for Manufacturing the Shame, Assignee: Agency for Science, Technology and Research, Patent

LT 601O B

US20130071058 A1, Mar 21, 2013]. A sophisticated multilayer structure consisting of layered germanium (Ge) and silicon (Si) waveguide, complex configuration of metal contacts and oxide layer is used. The German waveguide is also formed of several layers. The structure has two waveguides, the connection between which is made through a germanium waveguide. The disadvantages of the construction - complex production, inertness.

2. [Hideki Yagi; Method for manufacturing semiconductor optical modulator and semiconductor optical modulator, Assignee: Sumitomo Electric Industries, Ltd. (Osaka), Patent US20120308173 A1, Dec 06, 2012]. Using a sophisticated multilayer two-wire microstrip (MJL) structure consisting of a substrate of p-type and n-type semiconductor layers, the grounded layer can be made from an unalloyed semiconductor InP. The strips made of silicon nitride (SiN) or silica (S1O2) have a thickness of 300 nm. The disadvantage is the complexity of the construction.

3. [Toshio Baba et al. Optical modulator and method for manufacturing herein, Assignee: Nec Corporation, Patent US20120003767 A1, Jan 5, 2012]. The structure uses an open multilayer ribbed waveguide consisting of semiconductor and dielectric layers. The disadvantages are the complexity and inertness of the structure.

4. [Je Ha Kim et al. High Speed Semiconductor Optical Modulator and Fabricating Method Section, Assignee: Institute of Electronics and Telecommunication Research, Patent US6392781 B1, May 21, 2002], uses a sophisticated multilayer single-stranded MJL structure having waveguide channels of various sizes.

The dispersion characteristics of the plasma p-Ge waveguide were analyzed with the concentration of heavy holes in the semiconductor between 0 and 100% of the total charge carrier concentration Λ /, with a step of 5%. Here we have presented the dispersion characteristics of the p-Ge waveguide (Figs. 2, 3) at 70% concentration of heavy holes. The dispersion curves of the main (with the lowest crisis frequency) wave HEn and three higher type parasitic hybrid waves are presented. The phase characteristic of the waveguide is linear over a wide frequency range (Fig. 4). Waveguide rated frequency fr = 0.03-0.1 GHzm, constant magnetic flux density (magnetic induction) S _o = 1 T, total hole concentration N = 5-10 ¹⁹ m ³ , effective hole weight m * _h = 0.279m _e , effective mass of light holes m'i = 0,043m _e where m _e is mass of electron, mobility of heavy holes p ' _h = 6,3 m ² A / s, mobility of light holes μ * ι = 40,9 m ² / Vs.

The phase shift is calculated according to formula (1):

hV-ons, = l ^ - ^ l | _# = eo 's. ^X T '° ^<laiP) '^(1> where h 6o% and h 90% is the longitudinal propagation constant of the main wave type at 60% and 90% of the total charge carrier concentration in the waveguide respectively, L is the wavelength.

When fr = 0.09 GHzm, heo% = 7287 m ' ¹ , / 790% = 7328 m' ¹ , L = 10 cm, phase shift | Δ ^ | «235 °.

Claims (5)

DEFINITION OF INVENTION Optically controlled high speed broadband phase modulator consisting of an open waveguide with tapered ends (1) embedded in a metal cylindrical waveguide (2), a solenoid (3) generating a longitudinal permanent magnetic field H _o , and a dielectric frame (4), characterized by the fact that the plasma (gyro) electric semiconductor waveguide (1) has a cylindrical shape and is made of hole-permeable germanium (p-Ge), whose electromagnetic (EM) properties are highly dependent on the concentration ratio between heavy and light holes the source system (5) by varying the light intensity. 2. A modulator according to claim 1, characterized in that the normalized radius of the cylindrical plasma semiconductor waveguide is in the range fr = 0.030.1 GHz. 3. A modulator according to claims 1 and 2, characterized in that the concentration of heavy holes is varied from 60% to 90% of the total concentration of holes in the N waveguide. 4. A modulator according to claims 1-3, characterized in that the outer dielectric frame (4), consisting of a solenoid holder and a reflector, is a hollow cylinder made of an outer non-magnetic dielectric layer with a permanent longitudinal magnetic field generating a solenoid on its outer surface. 3), and the inner surface of the frame is a non-magnetic dielectric layer made of a material with a high relative dielectric permeability performing a reflector function, and the dielectric frame (4) and the light source system (5) are fixed to the waveguide. 5. A modulator according to claims 1-4, characterized in that the light source system (5) is composed of light sources of sufficient number and configuration, the light rays of which are concentrated by the lenses and incident on the surface of the p-Ge waveguide (1). intensity along the entire working length L surface, and the light intensity control system is controlled by a constant voltage which depends on the modulating signal.